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LU-3270 statahead: use dcache-like interface for sa entry
[fs/lustre-release.git] / lustre / llite / statahead.c
index 98c40e3..45bfe84 100644 (file)
@@ -27,7 +27,7 @@
  * Copyright (c) 2008, 2010, Oracle and/or its affiliates. All rights reserved.
  * Use is subject to license terms.
  *
- * Copyright (c) 2011, 2012, Intel Corporation.
+ * Copyright (c) 2011, 2013, Intel Corporation.
  */
 /*
  * This file is part of Lustre, http://www.lustre.org/
 #define DEBUG_SUBSYSTEM S_LLITE
 
 #include <obd_support.h>
-#include <lustre_lite.h>
 #include <lustre_dlm.h>
 #include "llite_internal.h"
 
 #define SA_OMITTED_ENTRY_MAX 8ULL
 
 typedef enum {
-        /** negative values are for error cases */
-        SA_ENTRY_INIT = 0,      /** init entry */
-        SA_ENTRY_SUCC = 1,      /** stat succeed */
-        SA_ENTRY_INVA = 2,      /** invalid entry */
-        SA_ENTRY_DEST = 3,      /** entry to be destroyed */
-} se_stat_t;
-
-struct ll_sa_entry {
-        /* link into sai->sai_entries_{sent,received,stated} */
-        cfs_list_t              se_list;
-        /* link into sai hash table locally */
-        cfs_list_t              se_hash;
-        /* entry reference count */
-        cfs_atomic_t            se_refcount;
-        /* entry index in the sai */
-        __u64                   se_index;
-        /* low layer ldlm lock handle */
-        __u64                   se_handle;
-        /* entry status */
-        se_stat_t               se_stat;
-        /* entry size, contains name */
-        int                     se_size;
-        /* pointer to async getattr enqueue info */
-        struct md_enqueue_info *se_minfo;
-        /* pointer to the async getattr request */
-        struct ptlrpc_request  *se_req;
-        /* pointer to the target inode */
-        struct inode           *se_inode;
-        /* entry name */
-        struct qstr             se_qstr;
+       /** negative values are for error cases */
+       SA_ENTRY_INIT = 0,      /** init entry */
+       SA_ENTRY_SUCC = 1,      /** stat succeed */
+       SA_ENTRY_INVA = 2,      /** invalid entry */
+} se_state_t;
+
+/* sa_entry is not refcounted: statahead thread allocates it and do async stat,
+ * and in async stat callback ll_statahead_interpret() will add it into
+ * sai_cb_entries, later statahead thread will call sa_handle_callback() to
+ * instantiate entry and move it into sai_entries, and then only scanner process
+ * can access and free it. */
+struct sa_entry {
+       /* link into sai_cb_entries or sai_entries */
+       struct list_head        se_list;
+       /* link into sai hash table locally */
+       struct list_head        se_hash;
+       /* entry index in the sai */
+       __u64                   se_index;
+       /* low layer ldlm lock handle */
+       __u64                   se_handle;
+       /* entry status */
+       se_state_t              se_state;
+       /* entry size, contains name */
+       int                     se_size;
+       /* pointer to async getattr enqueue info */
+       struct md_enqueue_info *se_minfo;
+       /* pointer to the async getattr request */
+       struct ptlrpc_request  *se_req;
+       /* pointer to the target inode */
+       struct inode           *se_inode;
+       /* entry name */
+       struct qstr             se_qstr;
 };
 
 static unsigned int sai_generation = 0;
 static DEFINE_SPINLOCK(sai_generation_lock);
 
-static inline int ll_sa_entry_unlinked(struct ll_sa_entry *entry)
+static inline int sa_unhashed(struct sa_entry *entry)
 {
-        return cfs_list_empty(&entry->se_list);
-}
-
-static inline int ll_sa_entry_unhashed(struct ll_sa_entry *entry)
-{
-        return cfs_list_empty(&entry->se_hash);
+       return list_empty(&entry->se_hash);
 }
 
 /*
  * The entry only can be released by the caller, it is necessary to hold lock.
  */
-static inline int ll_sa_entry_stated(struct ll_sa_entry *entry)
+static inline int sa_ready(struct sa_entry *entry)
 {
-        smp_rmb();
-        return (entry->se_stat != SA_ENTRY_INIT);
+       smp_rmb();
+       return (entry->se_state != SA_ENTRY_INIT);
 }
 
-static inline int ll_sa_entry_hash(int val)
+static inline int sa_hash(int val)
 {
-        return val & LL_SA_CACHE_MASK;
+       return val & LL_SA_CACHE_MASK;
 }
 
 /*
  * Insert entry to hash SA table.
  */
 static inline void
-ll_sa_entry_enhash(struct ll_statahead_info *sai, struct ll_sa_entry *entry)
+sa_rehash(struct ll_statahead_info *sai, struct sa_entry *entry)
 {
-       int i = ll_sa_entry_hash(entry->se_qstr.hash);
+       int i = sa_hash(entry->se_qstr.hash);
 
        spin_lock(&sai->sai_cache_lock[i]);
-       cfs_list_add_tail(&entry->se_hash, &sai->sai_cache[i]);
+       list_add_tail(&entry->se_hash, &sai->sai_cache[i]);
        spin_unlock(&sai->sai_cache_lock[i]);
 }
 
@@ -126,12 +122,12 @@ ll_sa_entry_enhash(struct ll_statahead_info *sai, struct ll_sa_entry *entry)
  * Remove entry from SA table.
  */
 static inline void
-ll_sa_entry_unhash(struct ll_statahead_info *sai, struct ll_sa_entry *entry)
+sa_unhash(struct ll_statahead_info *sai, struct sa_entry *entry)
 {
-       int i = ll_sa_entry_hash(entry->se_qstr.hash);
+       int i = sa_hash(entry->se_qstr.hash);
 
        spin_lock(&sai->sai_cache_lock[i]);
-       cfs_list_del_init(&entry->se_hash);
+       list_del_init(&entry->se_hash);
        spin_unlock(&sai->sai_cache_lock[i]);
 }
 
@@ -141,33 +137,26 @@ static inline int agl_should_run(struct ll_statahead_info *sai,
        return (inode != NULL && S_ISREG(inode->i_mode) && sai->sai_agl_valid);
 }
 
-static inline struct ll_sa_entry *
-sa_first_received_entry(struct ll_statahead_info *sai)
-{
-        return cfs_list_entry(sai->sai_entries_received.next,
-                              struct ll_sa_entry, se_list);
-}
-
 static inline struct ll_inode_info *
 agl_first_entry(struct ll_statahead_info *sai)
 {
-        return cfs_list_entry(sai->sai_entries_agl.next,
-                              struct ll_inode_info, lli_agl_list);
+       return list_entry(sai->sai_agls.next, struct ll_inode_info,
+                         lli_agl_list);
 }
 
 static inline int sa_sent_full(struct ll_statahead_info *sai)
 {
-        return cfs_atomic_read(&sai->sai_cache_count) >= sai->sai_max;
+       return atomic_read(&sai->sai_cache_count) >= sai->sai_max;
 }
 
-static inline int sa_received_empty(struct ll_statahead_info *sai)
+static inline int sa_has_callback(struct ll_statahead_info *sai)
 {
-        return cfs_list_empty(&sai->sai_entries_received);
+       return !list_empty(&sai->sai_interim_entries);
 }
 
 static inline int agl_list_empty(struct ll_statahead_info *sai)
 {
-        return cfs_list_empty(&sai->sai_entries_agl);
+       return list_empty(&sai->sai_agls);
 }
 
 /**
@@ -192,253 +181,187 @@ static inline int is_omitted_entry(struct ll_statahead_info *sai, __u64 index)
                  sai->sai_index);
 }
 
-/*
- * Insert it into sai_entries_sent tail when init.
- */
-static struct ll_sa_entry *
-ll_sa_entry_alloc(struct ll_statahead_info *sai, __u64 index,
-                  const char *name, int len)
+/* allocate sa_entry and add it into hash to let scanner process to find it */
+static struct sa_entry *
+sa_alloc(struct ll_statahead_info *sai, __u64 index, const char *name, int len)
 {
-        struct ll_inode_info *lli;
-        struct ll_sa_entry   *entry;
-        int                   entry_size;
-        char                 *dname;
-        ENTRY;
-
-        entry_size = sizeof(struct ll_sa_entry) + (len & ~3) + 4;
-        OBD_ALLOC(entry, entry_size);
-        if (unlikely(entry == NULL))
-                RETURN(ERR_PTR(-ENOMEM));
-
-        CDEBUG(D_READA, "alloc sai entry %.*s(%p) index "LPU64"\n",
-               len, name, entry, index);
-
-        entry->se_index = index;
-
-        /*
-         * Statahead entry reference rules:
-         *
-         * 1) When statahead entry is initialized, its reference is set as 2.
-         *    One reference is used by the directory scanner. When the scanner
-         *    searches the statahead cache for the given name, it can perform
-         *    lockless hash lookup (only the scanner can remove entry from hash
-         *    list), and once found, it needn't to call "atomic_inc()" for the
-         *    entry reference. So the performance is improved. After using the
-         *    statahead entry, the scanner will call "atomic_dec()" to drop the
-         *    reference held when initialization. If it is the last reference,
-         *    the statahead entry will be freed.
-         *
-         * 2) All other threads, including statahead thread and ptlrpcd thread,
-         *    when they process the statahead entry, the reference for target
-         *    should be held to guarantee the entry will not be released by the
-         *    directory scanner. After processing the entry, these threads will
-         *    drop the entry reference. If it is the last reference, the entry
-         *    will be freed.
-         *
-         *    The second reference when initializes the statahead entry is used
-         *    by the statahead thread, following the rule 2).
-         */
-        cfs_atomic_set(&entry->se_refcount, 2);
-        entry->se_stat = SA_ENTRY_INIT;
-        entry->se_size = entry_size;
-        dname = (char *)entry + sizeof(struct ll_sa_entry);
-        memcpy(dname, name, len);
-        dname[len] = 0;
-        entry->se_qstr.hash = full_name_hash(name, len);
-        entry->se_qstr.len = len;
-        entry->se_qstr.name = dname;
-
-        lli = ll_i2info(sai->sai_inode);
+       struct ll_inode_info *lli;
+       struct sa_entry *entry;
+       int entry_size;
+       char *dname;
+       ENTRY;
+
+       entry_size = sizeof(struct sa_entry) + (len & ~3) + 4;
+       OBD_ALLOC(entry, entry_size);
+       if (unlikely(entry == NULL))
+               RETURN(ERR_PTR(-ENOMEM));
+
+       CDEBUG(D_READA, "alloc sa entry %.*s(%p) index "LPU64"\n",
+              len, name, entry, index);
+
+       entry->se_index = index;
+
+       entry->se_state = SA_ENTRY_INIT;
+       entry->se_size = entry_size;
+       dname = (char *)entry + sizeof(struct sa_entry);
+       memcpy(dname, name, len);
+       dname[len] = 0;
+       entry->se_qstr.hash = full_name_hash(name, len);
+       entry->se_qstr.len = len;
+       entry->se_qstr.name = dname;
+
+       lli = ll_i2info(sai->sai_inode);
        spin_lock(&lli->lli_sa_lock);
-       cfs_list_add_tail(&entry->se_list, &sai->sai_entries_sent);
+       INIT_LIST_HEAD(&entry->se_list);
+       sa_rehash(sai, entry);
        spin_unlock(&lli->lli_sa_lock);
 
-       cfs_atomic_inc(&sai->sai_cache_count);
-       ll_sa_entry_enhash(sai, entry);
+       atomic_inc(&sai->sai_cache_count);
 
        RETURN(entry);
 }
 
-/*
- * Used by the directory scanner to search entry with name.
- *
- * Only the caller can remove the entry from hash, so it is unnecessary to hold
- * hash lock. It is caller's duty to release the init refcount on the entry, so
- * it is also unnecessary to increase refcount on the entry.
- */
-static struct ll_sa_entry *
-ll_sa_entry_get_byname(struct ll_statahead_info *sai, const struct qstr *qstr)
+/* free sa_entry which should have been unhashed and not in any list */
+static void sa_free(struct ll_statahead_info *sai, struct sa_entry *entry)
 {
-        struct ll_sa_entry *entry;
-        int i = ll_sa_entry_hash(qstr->hash);
-
-        cfs_list_for_each_entry(entry, &sai->sai_cache[i], se_hash) {
-                if (entry->se_qstr.hash == qstr->hash &&
-                    entry->se_qstr.len == qstr->len &&
-                    memcmp(entry->se_qstr.name, qstr->name, qstr->len) == 0)
-                        return entry;
-        }
-        return NULL;
-}
+       CDEBUG(D_READA, "free sa entry %.*s(%p) index "LPU64"\n",
+              entry->se_qstr.len, entry->se_qstr.name, entry,
+              entry->se_index);
 
-/*
- * Used by the async getattr request callback to find entry with index.
- *
- * Inside lli_sa_lock to prevent others to change the list during the search.
- * It needs to increase entry refcount before returning to guarantee that the
- * entry cannot be freed by others.
- */
-static struct ll_sa_entry *
-ll_sa_entry_get_byindex(struct ll_statahead_info *sai, __u64 index)
-{
-        struct ll_sa_entry *entry;
-
-        cfs_list_for_each_entry(entry, &sai->sai_entries_sent, se_list) {
-                if (entry->se_index == index) {
-                        cfs_atomic_inc(&entry->se_refcount);
-                        return entry;
-                }
-                if (entry->se_index > index)
-                        break;
-        }
-        return NULL;
-}
-
-static void ll_sa_entry_cleanup(struct ll_statahead_info *sai,
-                                 struct ll_sa_entry *entry)
-{
-        struct md_enqueue_info *minfo = entry->se_minfo;
-        struct ptlrpc_request  *req   = entry->se_req;
-
-        if (minfo) {
-                entry->se_minfo = NULL;
-                ll_intent_release(&minfo->mi_it);
-                iput(minfo->mi_dir);
-                OBD_FREE_PTR(minfo);
-        }
+       LASSERT(list_empty(&entry->se_list));
+       LASSERT(sa_unhashed(entry));
 
-        if (req) {
-                entry->se_req = NULL;
-                ptlrpc_req_finished(req);
-        }
+       OBD_FREE(entry, entry->se_size);
+       atomic_dec(&sai->sai_cache_count);
 }
 
-static void ll_sa_entry_put(struct ll_statahead_info *sai,
-                             struct ll_sa_entry *entry)
+/* find sa_entry by name, used by directory scanner, lock is not needed because
+ * only scanner can remove the entry from hash.
+ */
+static struct sa_entry *
+sa_get(struct ll_statahead_info *sai, const struct qstr *qstr)
 {
-        if (cfs_atomic_dec_and_test(&entry->se_refcount)) {
-                CDEBUG(D_READA, "free sai entry %.*s(%p) index "LPU64"\n",
-                       entry->se_qstr.len, entry->se_qstr.name, entry,
-                       entry->se_index);
-
-                LASSERT(ll_sa_entry_unhashed(entry));
-                LASSERT(ll_sa_entry_unlinked(entry));
-
-                ll_sa_entry_cleanup(sai, entry);
-                if (entry->se_inode)
-                        iput(entry->se_inode);
-
-                OBD_FREE(entry, entry->se_size);
-                cfs_atomic_dec(&sai->sai_cache_count);
-        }
+       struct sa_entry *entry;
+       int i = sa_hash(qstr->hash);
+
+       list_for_each_entry(entry, &sai->sai_cache[i], se_hash) {
+               if (entry->se_qstr.hash == qstr->hash &&
+                   entry->se_qstr.len == qstr->len &&
+                   memcmp(entry->se_qstr.name, qstr->name, qstr->len) == 0)
+                       return entry;
+       }
+       return NULL;
 }
 
 static inline void
-do_sai_entry_fini(struct ll_statahead_info *sai, struct ll_sa_entry *entry)
+sa_kill(struct ll_statahead_info *sai, struct sa_entry *entry)
 {
        struct ll_inode_info *lli = ll_i2info(sai->sai_inode);
 
-       ll_sa_entry_unhash(sai, entry);
+       LASSERT(!sa_unhashed(entry));
+       LASSERT(!list_empty(&entry->se_list));
+       LASSERT(sa_ready(entry));
+
+       sa_unhash(sai, entry);
 
        spin_lock(&lli->lli_sa_lock);
-       entry->se_stat = SA_ENTRY_DEST;
-       if (likely(!ll_sa_entry_unlinked(entry)))
-               cfs_list_del_init(&entry->se_list);
+       list_del_init(&entry->se_list);
        spin_unlock(&lli->lli_sa_lock);
 
-       ll_sa_entry_put(sai, entry);
+       if (entry->se_inode != NULL)
+               iput(entry->se_inode);
+
+       sa_free(sai, entry);
 }
 
-/*
- * Delete it from sai_entries_stated list when fini.
- */
+/* called by scanner after use, sa_entry will be killed */
 static void
-ll_sa_entry_fini(struct ll_statahead_info *sai, struct ll_sa_entry *entry)
+sa_put(struct ll_statahead_info *sai, struct sa_entry *entry)
 {
-        struct ll_sa_entry *pos, *next;
+       struct sa_entry *tmp, *next;
 
-        if (entry)
-                do_sai_entry_fini(sai, entry);
+       if (entry != NULL && entry->se_state == SA_ENTRY_SUCC) {
+               struct ll_sb_info *sbi = ll_i2sbi(sai->sai_inode);
 
-        /* drop old entry from sent list */
-        cfs_list_for_each_entry_safe(pos, next, &sai->sai_entries_sent,
-                                     se_list) {
-                if (is_omitted_entry(sai, pos->se_index))
-                        do_sai_entry_fini(sai, pos);
-                else
-                        break;
-        }
+               sai->sai_hit++;
+               sai->sai_consecutive_miss = 0;
+               sai->sai_max = min(2 * sai->sai_max, sbi->ll_sa_max);
+       } else {
+               sai->sai_miss++;
+               sai->sai_consecutive_miss++;
+       }
 
-        /* drop old entry from stated list */
-        cfs_list_for_each_entry_safe(pos, next, &sai->sai_entries_stated,
-                                     se_list) {
-                if (is_omitted_entry(sai, pos->se_index))
-                        do_sai_entry_fini(sai, pos);
-                else
-                        break;
-        }
+       if (entry != NULL)
+               sa_kill(sai, entry);
+
+       /* kill old completed entries, only scanner process does this, no need
+        * to lock */
+       list_for_each_entry_safe(tmp, next, &sai->sai_entries, se_list) {
+               if (!is_omitted_entry(sai, tmp->se_index))
+                       break;
+               sa_kill(sai, tmp);
+       }
+
+       wake_up(&sai->sai_thread.t_ctl_waitq);
 }
 
-/*
- * Inside lli_sa_lock.
- */
-static void
-do_sai_entry_to_stated(struct ll_statahead_info *sai,
-                       struct ll_sa_entry *entry, int rc)
+/* update state and sort add entry to sai_entries by index, return true if
+ * scanner is waiting on this entry. */
+static bool
+__sa_make_ready(struct ll_statahead_info *sai, struct sa_entry *entry, int ret)
 {
-        struct ll_sa_entry *se;
-        cfs_list_t         *pos = &sai->sai_entries_stated;
+       struct sa_entry *se;
+       struct list_head *pos = &sai->sai_entries;
 
-        if (!ll_sa_entry_unlinked(entry))
-                cfs_list_del_init(&entry->se_list);
+       LASSERT(!sa_ready(entry));
+       LASSERT(list_empty(&entry->se_list));
 
-        cfs_list_for_each_entry_reverse(se, &sai->sai_entries_stated, se_list) {
-                if (se->se_index < entry->se_index) {
-                        pos = &se->se_list;
-                        break;
-                }
-        }
+       entry->se_state = ret < 0 ? SA_ENTRY_INVA : SA_ENTRY_SUCC;
+
+       list_for_each_entry_reverse(se, &sai->sai_entries, se_list) {
+               if (se->se_index < entry->se_index) {
+                       pos = &se->se_list;
+                       break;
+               }
+       }
+       list_add(&entry->se_list, pos);
 
-        cfs_list_add(&entry->se_list, pos);
-        entry->se_stat = rc;
+       return (entry->se_index == sai->sai_index_wait);
 }
 
-/*
- * Move entry to sai_entries_stated and sort with the index.
- * \retval 1    -- entry to be destroyed.
- * \retval 0    -- entry is inserted into stated list.
- */
-static int
-ll_sa_entry_to_stated(struct ll_statahead_info *sai,
-                     struct ll_sa_entry *entry, int rc)
+/* release resources used in async stat RPC, complete entry information and
+ * wakeup if necessary */
+static void
+sa_make_ready(struct ll_statahead_info *sai, struct sa_entry *entry, int ret)
 {
        struct ll_inode_info *lli = ll_i2info(sai->sai_inode);
-       int                   ret = 1;
+       struct md_enqueue_info *minfo = entry->se_minfo;
+       struct ptlrpc_request *req = entry->se_req;
+       bool wakeup;
+
+       /* release resources used in RPC */
+       if (minfo) {
+               entry->se_minfo = NULL;
+               ll_intent_release(&minfo->mi_it);
+               iput(minfo->mi_dir);
+               OBD_FREE_PTR(minfo);
+       }
 
-       ll_sa_entry_cleanup(sai, entry);
+       if (req) {
+               entry->se_req = NULL;
+               ptlrpc_req_finished(req);
+       }
 
        spin_lock(&lli->lli_sa_lock);
-       if (likely(entry->se_stat != SA_ENTRY_DEST)) {
-               do_sai_entry_to_stated(sai, entry, rc);
-               ret = 0;
-       }
+       wakeup = __sa_make_ready(sai, entry, ret);
        spin_unlock(&lli->lli_sa_lock);
 
-       return ret;
+       if (wakeup)
+               wake_up(&sai->sai_waitq);
 }
 
 /*
- * Insert inode into the list of sai_entries_agl.
+ * Insert inode into the list of sai_agls.
  */
 static void ll_agl_add(struct ll_statahead_info *sai,
                        struct inode *inode, int index)
@@ -452,33 +375,33 @@ static void ll_agl_add(struct ll_statahead_info *sai,
                child->lli_agl_index = index;
                spin_unlock(&child->lli_agl_lock);
 
-               LASSERT(cfs_list_empty(&child->lli_agl_list));
+               LASSERT(list_empty(&child->lli_agl_list));
 
                igrab(inode);
                spin_lock(&parent->lli_agl_lock);
                if (agl_list_empty(sai))
                        added = 1;
-               cfs_list_add_tail(&child->lli_agl_list, &sai->sai_entries_agl);
+               list_add_tail(&child->lli_agl_list, &sai->sai_agls);
                spin_unlock(&parent->lli_agl_lock);
        } else {
                spin_unlock(&child->lli_agl_lock);
        }
 
        if (added > 0)
-               cfs_waitq_signal(&sai->sai_agl_thread.t_ctl_waitq);
+               wake_up(&sai->sai_agl_thread.t_ctl_waitq);
 }
 
 static struct ll_statahead_info *ll_sai_alloc(void)
 {
-        struct ll_statahead_info *sai;
-        int                       i;
-        ENTRY;
+       struct ll_statahead_info *sai;
+       int                       i;
+       ENTRY;
 
-        OBD_ALLOC_PTR(sai);
-        if (!sai)
-                RETURN(NULL);
+       OBD_ALLOC_PTR(sai);
+       if (!sai)
+               RETURN(NULL);
 
-        cfs_atomic_set(&sai->sai_refcount, 1);
+       atomic_set(&sai->sai_refcount, 1);
 
        spin_lock(&sai_generation_lock);
        sai->sai_generation = ++sai_generation;
@@ -486,92 +409,77 @@ static struct ll_statahead_info *ll_sai_alloc(void)
                sai->sai_generation = ++sai_generation;
        spin_unlock(&sai_generation_lock);
 
-        sai->sai_max = LL_SA_RPC_MIN;
-        sai->sai_index = 1;
-        cfs_waitq_init(&sai->sai_waitq);
-        cfs_waitq_init(&sai->sai_thread.t_ctl_waitq);
-        cfs_waitq_init(&sai->sai_agl_thread.t_ctl_waitq);
+       sai->sai_max = LL_SA_RPC_MIN;
+       sai->sai_index = 1;
+       init_waitqueue_head(&sai->sai_waitq);
+       init_waitqueue_head(&sai->sai_thread.t_ctl_waitq);
+       init_waitqueue_head(&sai->sai_agl_thread.t_ctl_waitq);
 
-        CFS_INIT_LIST_HEAD(&sai->sai_entries_sent);
-        CFS_INIT_LIST_HEAD(&sai->sai_entries_received);
-        CFS_INIT_LIST_HEAD(&sai->sai_entries_stated);
-        CFS_INIT_LIST_HEAD(&sai->sai_entries_agl);
+       INIT_LIST_HEAD(&sai->sai_interim_entries);
+       INIT_LIST_HEAD(&sai->sai_entries);
+       INIT_LIST_HEAD(&sai->sai_agls);
 
-        for (i = 0; i < LL_SA_CACHE_SIZE; i++) {
-                CFS_INIT_LIST_HEAD(&sai->sai_cache[i]);
+       for (i = 0; i < LL_SA_CACHE_SIZE; i++) {
+               INIT_LIST_HEAD(&sai->sai_cache[i]);
                spin_lock_init(&sai->sai_cache_lock[i]);
-        }
-        cfs_atomic_set(&sai->sai_cache_count, 0);
+       }
+       atomic_set(&sai->sai_cache_count, 0);
 
-        RETURN(sai);
+       RETURN(sai);
 }
 
-static inline struct ll_statahead_info *
-ll_sai_get(struct ll_statahead_info *sai)
+static inline struct ll_statahead_info *ll_sai_get(struct inode *dir)
 {
-        cfs_atomic_inc(&sai->sai_refcount);
-        return sai;
+       struct ll_inode_info *lli = ll_i2info(dir);
+       struct ll_statahead_info *sai = NULL;
+
+       spin_lock(&lli->lli_sa_lock);
+       sai = lli->lli_sai;
+       if (sai != NULL)
+               atomic_inc(&sai->sai_refcount);
+       spin_unlock(&lli->lli_sa_lock);
+
+       return sai;
 }
 
 static void ll_sai_put(struct ll_statahead_info *sai)
 {
-        struct inode         *inode = sai->sai_inode;
-        struct ll_inode_info *lli   = ll_i2info(inode);
-        ENTRY;
-
-        if (cfs_atomic_dec_and_lock(&sai->sai_refcount, &lli->lli_sa_lock)) {
-                struct ll_sa_entry *entry, *next;
-
-                if (unlikely(cfs_atomic_read(&sai->sai_refcount) > 0)) {
-                        /* It is race case, the interpret callback just hold
-                         * a reference count */
-                       spin_unlock(&lli->lli_sa_lock);
-                       RETURN_EXIT;
-               }
+       struct ll_inode_info *lli = ll_i2info(sai->sai_inode);
 
-               LASSERT(lli->lli_opendir_key == NULL);
-               LASSERT(thread_is_stopped(&sai->sai_thread));
-               LASSERT(thread_is_stopped(&sai->sai_agl_thread));
+       if (atomic_dec_and_lock(&sai->sai_refcount, &lli->lli_sa_lock)) {
+               struct sa_entry *entry, *next;
+               struct ll_sb_info *sbi = ll_i2sbi(sai->sai_inode);
 
                lli->lli_sai = NULL;
-               lli->lli_opendir_pid = 0;
                spin_unlock(&lli->lli_sa_lock);
 
-                if (sai->sai_sent > sai->sai_replied)
-                        CDEBUG(D_READA,"statahead for dir "DFID" does not "
-                              "finish: [sent:"LPU64"] [replied:"LPU64"]\n",
-                              PFID(&lli->lli_fid),
-                              sai->sai_sent, sai->sai_replied);
-
-                cfs_list_for_each_entry_safe(entry, next,
-                                             &sai->sai_entries_sent, se_list)
-                        do_sai_entry_fini(sai, entry);
-
-                LASSERT(sa_received_empty(sai));
+               LASSERT(thread_is_stopped(&sai->sai_thread));
+               LASSERT(thread_is_stopped(&sai->sai_agl_thread));
+               LASSERT(sai->sai_sent == sai->sai_replied);
+               LASSERT(!sa_has_callback(sai));
 
-                cfs_list_for_each_entry_safe(entry, next,
-                                             &sai->sai_entries_stated, se_list)
-                        do_sai_entry_fini(sai, entry);
+               list_for_each_entry_safe(entry, next, &sai->sai_entries,
+                                        se_list)
+                       sa_kill(sai, entry);
 
-                LASSERT(cfs_atomic_read(&sai->sai_cache_count) == 0);
-                LASSERT(agl_list_empty(sai));
+               LASSERT(atomic_read(&sai->sai_cache_count) == 0);
+               LASSERT(agl_list_empty(sai));
 
-                iput(inode);
-                OBD_FREE_PTR(sai);
-        }
-
-        EXIT;
+               iput(sai->sai_inode);
+               OBD_FREE_PTR(sai);
+               atomic_dec(&sbi->ll_sa_running);
+       }
 }
 
-/* Do NOT forget to drop inode refcount when into sai_entries_agl. */
+/* Do NOT forget to drop inode refcount when into sai_agls. */
 static void ll_agl_trigger(struct inode *inode, struct ll_statahead_info *sai)
 {
-        struct ll_inode_info *lli   = ll_i2info(inode);
-        __u64                 index = lli->lli_agl_index;
-        int                   rc;
-        ENTRY;
+       struct ll_inode_info *lli = ll_i2info(inode);
+       __u64 index = lli->lli_agl_index;
+       int rc;
+       ENTRY;
 
-        LASSERT(cfs_list_empty(&lli->lli_agl_list));
+       LASSERT(list_empty(&lli->lli_agl_list));
 
         /* AGL maybe fall behind statahead with one entry */
         if (is_omitted_entry(sai, index + 1)) {
@@ -626,34 +534,19 @@ static void ll_agl_trigger(struct inode *inode, struct ll_statahead_info *sai)
         EXIT;
 }
 
-static void do_statahead_interpret(struct ll_statahead_info *sai,
-                                   struct ll_sa_entry *target)
+/* prepare inode for sa entry, add it into agl list, now sa_entry is ready
+ * to be used by scanner process. */
+static void sa_instantiate(struct ll_statahead_info *sai,
+                                struct sa_entry *entry)
 {
-        struct inode           *dir   = sai->sai_inode;
-        struct inode           *child;
-        struct ll_inode_info   *lli   = ll_i2info(dir);
-        struct ll_sa_entry     *entry;
-        struct md_enqueue_info *minfo;
-        struct lookup_intent   *it;
-        struct ptlrpc_request  *req;
-        struct mdt_body        *body;
-        int                     rc    = 0;
-        ENTRY;
-
-       spin_lock(&lli->lli_sa_lock);
-       if (target != NULL && target->se_req != NULL &&
-           !cfs_list_empty(&target->se_list)) {
-               entry = target;
-       } else if (unlikely(sa_received_empty(sai))) {
-               spin_unlock(&lli->lli_sa_lock);
-               RETURN_EXIT;
-       } else {
-               entry = sa_first_received_entry(sai);
-       }
-
-       cfs_atomic_inc(&entry->se_refcount);
-       cfs_list_del_init(&entry->se_list);
-       spin_unlock(&lli->lli_sa_lock);
+       struct inode *dir = sai->sai_inode;
+       struct inode *child;
+       struct md_enqueue_info *minfo;
+       struct lookup_intent *it;
+       struct ptlrpc_request *req;
+       struct mdt_body *body;
+       int rc = 0;
+       ENTRY;
 
         LASSERT(entry->se_handle != 0);
 
@@ -673,14 +566,15 @@ static void do_statahead_interpret(struct ll_statahead_info *sai,
 
                 /* XXX: No fid in reply, this is probaly cross-ref case.
                  * SA can't handle it yet. */
-                if (body->valid & OBD_MD_MDS)
-                        GOTO(out, rc = -EAGAIN);
-        } else {
-                /*
-                 * revalidate.
-                 */
-                /* unlinked and re-created with the same name */
-                if (unlikely(!lu_fid_eq(&minfo->mi_data.op_fid2, &body->fid1))){
+               if (body->mbo_valid & OBD_MD_MDS)
+                       GOTO(out, rc = -EAGAIN);
+       } else {
+               /*
+                * revalidate.
+                */
+               /* unlinked and re-created with the same name */
+               if (unlikely(!lu_fid_eq(&minfo->mi_data.op_fid2,
+                                       &body->mbo_fid1))) {
                         entry->se_inode = NULL;
                         iput(child);
                         child = NULL;
@@ -688,16 +582,18 @@ static void do_statahead_interpret(struct ll_statahead_info *sai,
         }
 
         it->d.lustre.it_lock_handle = entry->se_handle;
-        rc = md_revalidate_lock(ll_i2mdexp(dir), it, NULL, NULL);
+       rc = md_revalidate_lock(ll_i2mdexp(dir), it, ll_inode2fid(dir), NULL);
         if (rc != 1)
                 GOTO(out, rc = -EAGAIN);
 
-        rc = ll_prep_inode(&child, req, dir->i_sb);
+        rc = ll_prep_inode(&child, req, dir->i_sb, it);
         if (rc)
                 GOTO(out, rc);
 
-        CDEBUG(D_DLMTRACE, "setting l_data to inode %p (%lu/%u)\n",
-               child, child->i_ino, child->i_generation);
+       CDEBUG(D_READA, "%s: setting %.*s"DFID" l_data to inode %p\n",
+              ll_get_fsname(child->i_sb, NULL, 0),
+              entry->se_qstr.len, entry->se_qstr.name,
+              PFID(ll_inode2fid(child)), child);
         ll_set_lock_data(ll_i2sbi(dir)->ll_md_exp, child, it, NULL);
 
         entry->se_inode = child;
@@ -708,92 +604,105 @@ static void do_statahead_interpret(struct ll_statahead_info *sai,
         EXIT;
 
 out:
-        /* The "ll_sa_entry_to_stated()" will drop related ldlm ibits lock
-         * reference count by calling "ll_intent_drop_lock()" in spite of the
-         * above operations failed or not. Do not worry about calling
-         * "ll_intent_drop_lock()" more than once. */
-        rc = ll_sa_entry_to_stated(sai, entry, rc < 0 ? rc : SA_ENTRY_SUCC);
-        if (rc == 0 && entry->se_index == sai->sai_index_wait && target == NULL)
-                cfs_waitq_signal(&sai->sai_waitq);
-        ll_sa_entry_put(sai, entry);
+       /* sa_make_ready() will drop ldlm ibits lock refcount by calling
+        * ll_intent_drop_lock() in spite of failures. Do not worry about
+        * calling ll_intent_drop_lock() more than once. */
+       sa_make_ready(sai, entry, rc);
 }
 
-static int ll_statahead_interpret(struct ptlrpc_request *req,
-                                  struct md_enqueue_info *minfo, int rc)
+/* once there are async stat replies, instantiate sa_entry */
+static void sa_handle_callback(struct ll_statahead_info *sai)
 {
-        struct lookup_intent     *it  = &minfo->mi_it;
-        struct inode             *dir = minfo->mi_dir;
-        struct ll_inode_info     *lli = ll_i2info(dir);
-        struct ll_statahead_info *sai = NULL;
-        struct ll_sa_entry       *entry;
-        int                       wakeup;
-        ENTRY;
+       struct ll_inode_info *lli;
 
-        if (it_disposition(it, DISP_LOOKUP_NEG))
-                rc = -ENOENT;
+       lli = ll_i2info(sai->sai_inode);
 
-       spin_lock(&lli->lli_sa_lock);
-       /* stale entry */
-       if (unlikely(lli->lli_sai == NULL ||
-                    lli->lli_sai->sai_generation != minfo->mi_generation)) {
-               spin_unlock(&lli->lli_sa_lock);
-               GOTO(out, rc = -ESTALE);
-       } else {
-               sai = ll_sai_get(lli->lli_sai);
-               if (unlikely(!thread_is_running(&sai->sai_thread))) {
-                       sai->sai_replied++;
-                       spin_unlock(&lli->lli_sa_lock);
-                       GOTO(out, rc = -EBADFD);
-               }
+       while (sa_has_callback(sai)) {
+               struct sa_entry *entry;
 
-               entry = ll_sa_entry_get_byindex(sai, minfo->mi_cbdata);
-               if (entry == NULL) {
-                       sai->sai_replied++;
+               spin_lock(&lli->lli_sa_lock);
+               if (unlikely(!sa_has_callback(sai))) {
                        spin_unlock(&lli->lli_sa_lock);
-                       GOTO(out, rc = -EIDRM);
+                       break;
                }
+               entry = list_entry(sai->sai_interim_entries.next,
+                                  struct sa_entry, se_list);
+               list_del_init(&entry->se_list);
+               spin_unlock(&lli->lli_sa_lock);
 
-               cfs_list_del_init(&entry->se_list);
-               if (rc != 0) {
-                       sai->sai_replied++;
-                       do_sai_entry_to_stated(sai, entry, rc);
-                       spin_unlock(&lli->lli_sa_lock);
-                        if (entry->se_index == sai->sai_index_wait)
-                                cfs_waitq_signal(&sai->sai_waitq);
-                } else {
-                        entry->se_minfo = minfo;
-                        entry->se_req = ptlrpc_request_addref(req);
-                        /* Release the async ibits lock ASAP to avoid deadlock
-                         * when statahead thread tries to enqueue lock on parent
-                         * for readpage and other tries to enqueue lock on child
-                         * with parent's lock held, for example: unlink. */
-                        entry->se_handle = it->d.lustre.it_lock_handle;
-                        ll_intent_drop_lock(it);
-                        wakeup = sa_received_empty(sai);
-                        cfs_list_add_tail(&entry->se_list,
-                                          &sai->sai_entries_received);
-                        sai->sai_replied++;
-                       spin_unlock(&lli->lli_sa_lock);
-                        if (wakeup)
-                                cfs_waitq_signal(&sai->sai_thread.t_ctl_waitq);
-                }
-                ll_sa_entry_put(sai, entry);
-        }
+               sa_instantiate(sai, entry);
+       }
 
-        EXIT;
+       spin_lock(&lli->lli_agl_lock);
+       while (!agl_list_empty(sai)) {
+               struct ll_inode_info *clli;
 
-out:
-        if (rc != 0) {
-                ll_intent_release(it);
-                iput(dir);
-                OBD_FREE_PTR(minfo);
-        }
-        if (sai != NULL)
-                ll_sai_put(sai);
-        return rc;
+               clli = agl_first_entry(sai);
+               list_del_init(&clli->lli_agl_list);
+               spin_unlock(&lli->lli_agl_lock);
+
+               ll_agl_trigger(&clli->lli_vfs_inode, sai);
+
+               spin_lock(&lli->lli_agl_lock);
+       }
+       spin_unlock(&lli->lli_agl_lock);
 }
 
-static void sa_args_fini(struct md_enqueue_info *minfo,
+/* callback for async stat, because this is called in ptlrpcd context, we only
+ * put sa_entry in sai_cb_entries list, and let sa_handle_callback() to really
+ * prepare inode and instantiate sa_entry later. */
+static int ll_statahead_interpret(struct ptlrpc_request *req,
+                                 struct md_enqueue_info *minfo, int rc)
+{
+       struct lookup_intent *it = &minfo->mi_it;
+       struct inode *dir = minfo->mi_dir;
+       struct ll_inode_info *lli = ll_i2info(dir);
+       struct ll_statahead_info *sai = lli->lli_sai;
+       struct sa_entry *entry = (struct sa_entry *)minfo->mi_cbdata;
+       bool wakeup;
+       ENTRY;
+
+       if (it_disposition(it, DISP_LOOKUP_NEG))
+               rc = -ENOENT;
+
+       /* because statahead thread will wait for all inflight RPC to finish,
+        * sai should be always valid, no need to refcount */
+       LASSERT(sai != NULL);
+       LASSERT(!thread_is_stopped(&sai->sai_thread));
+       LASSERT(entry != NULL);
+
+       CDEBUG(D_READA, "sa_entry %.*s rc %d\n",
+              entry->se_qstr.len, entry->se_qstr.name, rc);
+
+       spin_lock(&lli->lli_sa_lock);
+       if (rc != 0) {
+               wakeup = __sa_make_ready(sai, entry, rc);
+       } else {
+               entry->se_minfo = minfo;
+               entry->se_req = ptlrpc_request_addref(req);
+               /* Release the async ibits lock ASAP to avoid deadlock
+                * when statahead thread tries to enqueue lock on parent
+                * for readpage and other tries to enqueue lock on child
+                * with parent's lock held, for example: unlink. */
+               entry->se_handle = it->d.lustre.it_lock_handle;
+               ll_intent_drop_lock(it);
+               wakeup = !sa_has_callback(sai);
+               list_add_tail(&entry->se_list, &sai->sai_interim_entries);
+       }
+       sai->sai_replied++;
+       if (wakeup)
+               wake_up(&sai->sai_thread.t_ctl_waitq);
+       spin_unlock(&lli->lli_sa_lock);
+
+       if (rc != 0) {
+               ll_intent_release(it);
+               iput(dir);
+               OBD_FREE_PTR(minfo);
+       }
+       RETURN(rc);
+}
+
+static void sa_fini_data(struct md_enqueue_info *minfo,
                          struct ldlm_enqueue_info *einfo)
 {
         LASSERT(minfo && einfo);
@@ -813,13 +722,12 @@ static void sa_args_fini(struct md_enqueue_info *minfo,
  * "ocapa". So here reserve "op_data.op_capa[1,2]" in "pcapa" before calling
  * "md_intent_getattr_async".
  */
-static int sa_args_init(struct inode *dir, struct inode *child,
-                        struct ll_sa_entry *entry, struct md_enqueue_info **pmi,
-                        struct ldlm_enqueue_info **pei,
-                        struct obd_capa **pcapa)
+static int sa_prep_data(struct inode *dir, struct inode *child,
+                       struct sa_entry *entry, struct md_enqueue_info **pmi,
+                       struct ldlm_enqueue_info **pei,
+                       struct obd_capa **pcapa)
 {
         struct qstr              *qstr = &entry->se_qstr;
-        struct ll_inode_info     *lli  = ll_i2info(dir);
         struct md_enqueue_info   *minfo;
         struct ldlm_enqueue_info *einfo;
         struct md_op_data        *op_data;
@@ -842,11 +750,10 @@ static int sa_args_init(struct inode *dir, struct inode *child,
                 return PTR_ERR(op_data);
         }
 
-        minfo->mi_it.it_op = IT_GETATTR;
-        minfo->mi_dir = igrab(dir);
-        minfo->mi_cb = ll_statahead_interpret;
-        minfo->mi_generation = lli->lli_sai->sai_generation;
-        minfo->mi_cbdata = entry->se_index;
+       minfo->mi_it.it_op = IT_GETATTR;
+       minfo->mi_dir = igrab(dir);
+       minfo->mi_cb = ll_statahead_interpret;
+       minfo->mi_cbdata = entry;
 
         einfo->ei_type   = LDLM_IBITS;
         einfo->ei_mode   = it_to_lock_mode(&minfo->mi_it);
@@ -863,27 +770,27 @@ static int sa_args_init(struct inode *dir, struct inode *child,
         return 0;
 }
 
-static int do_sa_lookup(struct inode *dir, struct ll_sa_entry *entry)
+static int sa_lookup(struct inode *dir, struct sa_entry *entry)
 {
-        struct md_enqueue_info   *minfo;
-        struct ldlm_enqueue_info *einfo;
-        struct obd_capa          *capas[2];
-        int                       rc;
-        ENTRY;
-
-        rc = sa_args_init(dir, NULL, entry, &minfo, &einfo, capas);
-        if (rc)
-                RETURN(rc);
-
-        rc = md_intent_getattr_async(ll_i2mdexp(dir), minfo, einfo);
-        if (!rc) {
-                capa_put(capas[0]);
-                capa_put(capas[1]);
-        } else {
-                sa_args_fini(minfo, einfo);
-        }
+       struct md_enqueue_info   *minfo;
+       struct ldlm_enqueue_info *einfo;
+       struct obd_capa          *capas[2];
+       int                       rc;
+       ENTRY;
+
+       rc = sa_prep_data(dir, NULL, entry, &minfo, &einfo, capas);
+       if (rc)
+               RETURN(rc);
+
+       rc = md_intent_getattr_async(ll_i2mdexp(dir), minfo, einfo);
+       if (!rc) {
+               capa_put(capas[0]);
+               capa_put(capas[1]);
+       } else {
+               sa_fini_data(minfo, einfo);
+       }
 
-        RETURN(rc);
+       RETURN(rc);
 }
 
 /**
@@ -892,127 +799,118 @@ static int do_sa_lookup(struct inode *dir, struct ll_sa_entry *entry)
  * \retval      0 -- will send stat-ahead request
  * \retval others -- prepare stat-ahead request failed
  */
-static int do_sa_revalidate(struct inode *dir, struct ll_sa_entry *entry,
-                            struct dentry *dentry)
+static int sa_revalidate(struct inode *dir, struct sa_entry *entry,
+                        struct dentry *dentry)
 {
-        struct inode             *inode = dentry->d_inode;
-        struct lookup_intent      it = { .it_op = IT_GETATTR,
-                                         .d.lustre.it_lock_handle = 0 };
-        struct md_enqueue_info   *minfo;
-        struct ldlm_enqueue_info *einfo;
-        struct obd_capa          *capas[2];
-        int rc;
-        ENTRY;
-
-        if (unlikely(inode == NULL))
-                RETURN(1);
-
-        if (d_mountpoint(dentry))
-                RETURN(1);
-
-        if (unlikely(dentry == dentry->d_sb->s_root))
-                RETURN(1);
-
-        entry->se_inode = igrab(inode);
-        rc = md_revalidate_lock(ll_i2mdexp(dir), &it, ll_inode2fid(inode),NULL);
-        if (rc == 1) {
-                entry->se_handle = it.d.lustre.it_lock_handle;
-                ll_intent_release(&it);
-                RETURN(1);
-        }
+       struct inode *inode = dentry->d_inode;
+       struct lookup_intent it = { .it_op = IT_GETATTR,
+                                   .d.lustre.it_lock_handle = 0 };
+       struct md_enqueue_info *minfo;
+       struct ldlm_enqueue_info *einfo;
+       struct obd_capa *capas[2];
+       int rc;
+       ENTRY;
+
+       if (unlikely(inode == NULL))
+               RETURN(1);
+
+       if (d_mountpoint(dentry))
+               RETURN(1);
+
+       entry->se_inode = igrab(inode);
+       rc = md_revalidate_lock(ll_i2mdexp(dir), &it, ll_inode2fid(inode),
+                               NULL);
+       if (rc == 1) {
+               entry->se_handle = it.d.lustre.it_lock_handle;
+               ll_intent_release(&it);
+               RETURN(1);
+       }
 
-        rc = sa_args_init(dir, inode, entry, &minfo, &einfo, capas);
-        if (rc) {
-                entry->se_inode = NULL;
-                iput(inode);
-                RETURN(rc);
-        }
+       rc = sa_prep_data(dir, inode, entry, &minfo, &einfo, capas);
+       if (rc) {
+               entry->se_inode = NULL;
+               iput(inode);
+               RETURN(rc);
+       }
 
-        rc = md_intent_getattr_async(ll_i2mdexp(dir), minfo, einfo);
-        if (!rc) {
-                capa_put(capas[0]);
-                capa_put(capas[1]);
-        } else {
-                entry->se_inode = NULL;
-                iput(inode);
-                sa_args_fini(minfo, einfo);
-        }
+       rc = md_intent_getattr_async(ll_i2mdexp(dir), minfo, einfo);
+       if (!rc) {
+               capa_put(capas[0]);
+               capa_put(capas[1]);
+       } else {
+               entry->se_inode = NULL;
+               iput(inode);
+               sa_fini_data(minfo, einfo);
+       }
 
-        RETURN(rc);
+       RETURN(rc);
 }
 
-static void ll_statahead_one(struct dentry *parent, const char* entry_name,
-                             int entry_name_len)
+static void sa_statahead(struct dentry *parent, const char *name, int len)
 {
-        struct inode             *dir    = parent->d_inode;
-        struct ll_inode_info     *lli    = ll_i2info(dir);
-        struct ll_statahead_info *sai    = lli->lli_sai;
-        struct dentry            *dentry = NULL;
-        struct ll_sa_entry       *entry;
-        int                       rc;
-        int                       rc1;
-        ENTRY;
-
-        entry = ll_sa_entry_alloc(sai, sai->sai_index, entry_name,
-                                  entry_name_len);
-        if (IS_ERR(entry))
-                RETURN_EXIT;
+       struct inode *dir = parent->d_inode;
+       struct ll_inode_info *lli = ll_i2info(dir);
+       struct ll_statahead_info *sai = lli->lli_sai;
+       struct dentry *dentry = NULL;
+       struct sa_entry *entry;
+       int rc;
+       ENTRY;
+
+       entry = sa_alloc(sai, sai->sai_index, name, len);
+       if (IS_ERR(entry))
+               RETURN_EXIT;
 
-        dentry = d_lookup(parent, &entry->se_qstr);
-        if (!dentry) {
-                rc = do_sa_lookup(dir, entry);
-        } else {
-                rc = do_sa_revalidate(dir, entry, dentry);
-                if (rc == 1 && agl_should_run(sai, dentry->d_inode))
-                        ll_agl_add(sai, dentry->d_inode, entry->se_index);
-        }
+       dentry = d_lookup(parent, &entry->se_qstr);
+       if (!dentry) {
+               rc = sa_lookup(dir, entry);
+       } else {
+               rc = sa_revalidate(dir, entry, dentry);
+               if (rc == 1 && agl_should_run(sai, dentry->d_inode))
+                       ll_agl_add(sai, dentry->d_inode, entry->se_index);
+       }
 
-        if (dentry != NULL)
-                dput(dentry);
+       if (dentry != NULL)
+               dput(dentry);
 
-        if (rc) {
-                rc1 = ll_sa_entry_to_stated(sai, entry,
-                                        rc < 0 ? SA_ENTRY_INVA : SA_ENTRY_SUCC);
-                if (rc1 == 0 && entry->se_index == sai->sai_index_wait)
-                        cfs_waitq_signal(&sai->sai_waitq);
-        } else {
-                sai->sai_sent++;
-        }
+       if (rc != 0)
+               sa_make_ready(sai, entry, rc);
+       else
+               sai->sai_sent++;
 
-        sai->sai_index++;
-        /* drop one refcount on entry by ll_sa_entry_alloc */
-        ll_sa_entry_put(sai, entry);
+       sai->sai_index++;
 
-        EXIT;
+       EXIT;
 }
 
 static int ll_agl_thread(void *arg)
 {
-        struct dentry            *parent = (struct dentry *)arg;
-        struct inode             *dir    = parent->d_inode;
-        struct ll_inode_info     *plli   = ll_i2info(dir);
-        struct ll_inode_info     *clli;
-        struct ll_sb_info        *sbi    = ll_i2sbi(dir);
-        struct ll_statahead_info *sai    = ll_sai_get(plli->lli_sai);
-        struct ptlrpc_thread     *thread = &sai->sai_agl_thread;
-        struct l_wait_info        lwi    = { 0 };
-        ENTRY;
-
-        {
-                char pname[16];
-                snprintf(pname, 15, "ll_agl_%u", plli->lli_opendir_pid);
-                cfs_daemonize(pname);
-        }
-
-        CDEBUG(D_READA, "agl thread started: [pid %d] [parent %.*s]\n",
-               cfs_curproc_pid(), parent->d_name.len, parent->d_name.name);
-
-        atomic_inc(&sbi->ll_agl_total);
+       struct dentry *parent = (struct dentry *)arg;
+       struct inode *dir = parent->d_inode;
+       struct ll_inode_info *plli = ll_i2info(dir);
+       struct ll_inode_info *clli;
+       struct ll_sb_info *sbi = ll_i2sbi(dir);
+       struct ll_statahead_info *sai;
+       struct ptlrpc_thread *thread;
+       struct l_wait_info lwi = { 0 };
+       ENTRY;
+
+
+       sai = ll_sai_get(dir);
+       thread = &sai->sai_agl_thread;
+       thread->t_pid = current_pid();
+       CDEBUG(D_READA, "agl thread started: sai %p, parent %.*s\n",
+              sai, parent->d_name.len, parent->d_name.name);
+
+       atomic_inc(&sbi->ll_agl_total);
        spin_lock(&plli->lli_agl_lock);
        sai->sai_agl_valid = 1;
-       thread_set_flags(thread, SVC_RUNNING);
+       if (thread_is_init(thread))
+               /* If someone else has changed the thread state
+                * (e.g. already changed to SVC_STOPPING), we can't just
+                * blindly overwrite that setting. */
+               thread_set_flags(thread, SVC_RUNNING);
        spin_unlock(&plli->lli_agl_lock);
-        cfs_waitq_signal(&thread->t_ctl_waitq);
+       wake_up(&thread->t_ctl_waitq);
 
         while (1) {
                 l_wait_event(thread->t_ctl_waitq,
@@ -1028,7 +926,7 @@ static int ll_agl_thread(void *arg)
                 * so check whether list empty again. */
                if (!agl_list_empty(sai)) {
                        clli = agl_first_entry(sai);
-                       cfs_list_del_init(&clli->lli_agl_list);
+                       list_del_init(&clli->lli_agl_list);
                        spin_unlock(&plli->lli_agl_lock);
                        ll_agl_trigger(&clli->lli_vfs_inode, sai);
                } else {
@@ -1040,7 +938,7 @@ static int ll_agl_thread(void *arg)
        sai->sai_agl_valid = 0;
        while (!agl_list_empty(sai)) {
                clli = agl_first_entry(sai);
-               cfs_list_del_init(&clli->lli_agl_list);
+               list_del_init(&clli->lli_agl_list);
                spin_unlock(&plli->lli_agl_lock);
                clli->lli_agl_index = 0;
                iput(&clli->lli_vfs_inode);
@@ -1048,328 +946,295 @@ static int ll_agl_thread(void *arg)
        }
        thread_set_flags(thread, SVC_STOPPED);
        spin_unlock(&plli->lli_agl_lock);
-       cfs_waitq_signal(&thread->t_ctl_waitq);
+       wake_up(&thread->t_ctl_waitq);
        ll_sai_put(sai);
-       CDEBUG(D_READA, "agl thread stopped: [pid %d] [parent %.*s]\n",
-              cfs_curproc_pid(), parent->d_name.len, parent->d_name.name);
+       CDEBUG(D_READA, "agl thread stopped: sai %p, parent %.*s\n",
+              sai, parent->d_name.len, parent->d_name.name);
        RETURN(0);
 }
 
 static void ll_start_agl(struct dentry *parent, struct ll_statahead_info *sai)
 {
-        struct ptlrpc_thread *thread = &sai->sai_agl_thread;
-        struct l_wait_info    lwi    = { 0 };
-        int                   rc;
-        ENTRY;
-
-        CDEBUG(D_READA, "start agl thread: [pid %d] [parent %.*s]\n",
-               cfs_curproc_pid(), parent->d_name.len, parent->d_name.name);
-
-        rc = cfs_create_thread(ll_agl_thread, parent, 0);
-        if (rc < 0) {
-                CERROR("can't start ll_agl thread, rc: %d\n", rc);
-                thread_set_flags(thread, SVC_STOPPED);
-                RETURN_EXIT;
-        }
+       struct ptlrpc_thread *thread = &sai->sai_agl_thread;
+       struct l_wait_info    lwi    = { 0 };
+       struct ll_inode_info  *plli;
+       struct task_struct            *task;
+       ENTRY;
+
+       CDEBUG(D_READA, "start agl thread: sai %p, parent %.*s\n",
+              sai, parent->d_name.len, parent->d_name.name);
+
+       plli = ll_i2info(parent->d_inode);
+       task = kthread_run(ll_agl_thread, parent,
+                              "ll_agl_%u", plli->lli_opendir_pid);
+       if (IS_ERR(task)) {
+               CERROR("can't start ll_agl thread, rc: %ld\n", PTR_ERR(task));
+               thread_set_flags(thread, SVC_STOPPED);
+               RETURN_EXIT;
+       }
 
-        l_wait_event(thread->t_ctl_waitq,
-                     thread_is_running(thread) || thread_is_stopped(thread),
-                     &lwi);
-        EXIT;
+       l_wait_event(thread->t_ctl_waitq,
+                    thread_is_running(thread) || thread_is_stopped(thread),
+                    &lwi);
+       EXIT;
 }
 
 static int ll_statahead_thread(void *arg)
 {
-        struct dentry            *parent = (struct dentry *)arg;
-        struct inode             *dir    = parent->d_inode;
-        struct ll_inode_info     *plli   = ll_i2info(dir);
-        struct ll_inode_info     *clli;
-        struct ll_sb_info        *sbi    = ll_i2sbi(dir);
-        struct ll_statahead_info *sai    = ll_sai_get(plli->lli_sai);
-        struct ptlrpc_thread     *thread = &sai->sai_thread;
-        struct ptlrpc_thread *agl_thread = &sai->sai_agl_thread;
-        struct page              *page;
-        __u64                     pos    = 0;
-        int                       first  = 0;
-        int                       rc     = 0;
-        struct ll_dir_chain       chain;
-        struct l_wait_info        lwi    = { 0 };
-        ENTRY;
-
-        {
-                char pname[16];
-                snprintf(pname, 15, "ll_sa_%u", plli->lli_opendir_pid);
-                cfs_daemonize(pname);
-        }
-
-        CDEBUG(D_READA, "statahead thread started: [pid %d] [parent %.*s]\n",
-               cfs_curproc_pid(), parent->d_name.len, parent->d_name.name);
-
-        if (sbi->ll_flags & LL_SBI_AGL_ENABLED)
-                ll_start_agl(parent, sai);
-
-        atomic_inc(&sbi->ll_sa_total);
-       spin_lock(&plli->lli_sa_lock);
-       thread_set_flags(thread, SVC_RUNNING);
-       spin_unlock(&plli->lli_sa_lock);
-       cfs_waitq_signal(&thread->t_ctl_waitq);
+       struct dentry *parent = (struct dentry *)arg;
+       struct inode *dir = parent->d_inode;
+       struct ll_inode_info *lli = ll_i2info(dir);
+       struct ll_sb_info *sbi = ll_i2sbi(dir);
+       struct ll_statahead_info *sai;
+       struct ptlrpc_thread *thread;
+       struct ptlrpc_thread *agl_thread;
+       int first = 0;
+       struct md_op_data *op_data;
+       struct ll_dir_chain chain;
+       struct l_wait_info lwi = { 0 };
+       struct page *page = NULL;
+       __u64 pos = 0;
+       int rc = 0;
+       ENTRY;
+
+       sai = ll_sai_get(dir);
+       thread = &sai->sai_thread;
+       agl_thread = &sai->sai_agl_thread;
+       thread->t_pid = current_pid();
+       CDEBUG(D_READA, "statahead thread starting: sai %p, parent %.*s\n",
+              sai, parent->d_name.len, parent->d_name.name);
+
+       op_data = ll_prep_md_op_data(NULL, dir, dir, NULL, 0, 0,
+                                    LUSTRE_OPC_ANY, dir);
+       if (IS_ERR(op_data))
+               GOTO(out, rc = PTR_ERR(op_data));
+
+       op_data->op_max_pages = ll_i2sbi(dir)->ll_md_brw_pages;
+
+       if (sbi->ll_flags & LL_SBI_AGL_ENABLED)
+               ll_start_agl(parent, sai);
+
+       atomic_inc(&sbi->ll_sa_total);
+       spin_lock(&lli->lli_sa_lock);
+       if (thread_is_init(thread))
+               /* If someone else has changed the thread state
+                * (e.g. already changed to SVC_STOPPING), we can't just
+                * blindly overwrite that setting. */
+               thread_set_flags(thread, SVC_RUNNING);
+       spin_unlock(&lli->lli_sa_lock);
+       wake_up(&thread->t_ctl_waitq);
 
        ll_dir_chain_init(&chain);
-       page = ll_get_dir_page(dir, pos, &chain);
-
-        while (1) {
-                struct lu_dirpage *dp;
-                struct lu_dirent  *ent;
-
-                if (IS_ERR(page)) {
-                        rc = PTR_ERR(page);
-                        CDEBUG(D_READA, "error reading dir "DFID" at "LPU64
-                               "/"LPU64": [rc %d] [parent %u]\n",
-                               PFID(ll_inode2fid(dir)), pos, sai->sai_index,
-                               rc, plli->lli_opendir_pid);
-                        GOTO(out, rc);
-                }
+       while (pos != MDS_DIR_END_OFF && thread_is_running(thread)) {
+               struct lu_dirpage *dp;
+               struct lu_dirent  *ent;
+
+               sai->sai_in_readpage = 1;
+               page = ll_get_dir_page(dir, op_data, pos, &chain);
+               sai->sai_in_readpage = 0;
+               if (IS_ERR(page)) {
+                       rc = PTR_ERR(page);
+                       CDEBUG(D_READA, "error reading dir "DFID" at "LPU64
+                              "/"LPU64" opendir_pid = %u: rc = %d\n",
+                              PFID(ll_inode2fid(dir)), pos, sai->sai_index,
+                              lli->lli_opendir_pid, rc);
+                       break;
+               }
 
-                dp = page_address(page);
-                for (ent = lu_dirent_start(dp); ent != NULL;
-                     ent = lu_dirent_next(ent)) {
-                        __u64 hash;
-                        int namelen;
-                        char *name;
-
-                        hash = le64_to_cpu(ent->lde_hash);
-                        if (unlikely(hash < pos))
-                                /*
-                                 * Skip until we find target hash value.
-                                 */
-                                continue;
-
-                        namelen = le16_to_cpu(ent->lde_namelen);
-                        if (unlikely(namelen == 0))
-                                /*
-                                 * Skip dummy record.
-                                 */
-                                continue;
-
-                        name = ent->lde_name;
-                        if (name[0] == '.') {
-                                if (namelen == 1) {
-                                        /*
-                                         * skip "."
-                                         */
-                                        continue;
-                                } else if (name[1] == '.' && namelen == 2) {
-                                        /*
-                                         * skip ".."
-                                         */
-                                        continue;
-                                } else if (!sai->sai_ls_all) {
-                                        /*
-                                         * skip hidden files.
-                                         */
-                                        sai->sai_skip_hidden++;
-                                        continue;
-                                }
-                        }
-
-                        /*
-                         * don't stat-ahead first entry.
-                         */
-                        if (unlikely(++first == 1))
-                                continue;
-
-keep_it:
-                        l_wait_event(thread->t_ctl_waitq,
-                                     !sa_sent_full(sai) ||
-                                     !sa_received_empty(sai) ||
-                                     !agl_list_empty(sai) ||
-                                     !thread_is_running(thread),
-                                     &lwi);
-
-interpret_it:
-                        while (!sa_received_empty(sai))
-                                do_statahead_interpret(sai, NULL);
-
-                        if (unlikely(!thread_is_running(thread))) {
-                                ll_release_page(page, 0);
-                                GOTO(out, rc = 0);
-                        }
-
-                        /* If no window for metadata statahead, but there are
-                         * some AGL entries to be triggered, then try to help
-                         * to process the AGL entries. */
-                        if (sa_sent_full(sai)) {
-                               spin_lock(&plli->lli_agl_lock);
-                               while (!agl_list_empty(sai)) {
-                                       clli = agl_first_entry(sai);
-                                       cfs_list_del_init(&clli->lli_agl_list);
-                                       spin_unlock(&plli->lli_agl_lock);
-                                        ll_agl_trigger(&clli->lli_vfs_inode,
-                                                       sai);
-
-                                        if (!sa_received_empty(sai))
-                                                goto interpret_it;
-
-                                        if (unlikely(
-                                                !thread_is_running(thread))) {
-                                                ll_release_page(page, 0);
-                                                GOTO(out, rc = 0);
-                                        }
-
-                                        if (!sa_sent_full(sai))
-                                                goto do_it;
-
-                                       spin_lock(&plli->lli_agl_lock);
+               dp = page_address(page);
+               for (ent = lu_dirent_start(dp);
+                    ent != NULL && thread_is_running(thread) &&
+                    !sa_low_hit(sai);
+                    ent = lu_dirent_next(ent)) {
+                       __u64 hash;
+                       int namelen;
+                       char *name;
+
+                       hash = le64_to_cpu(ent->lde_hash);
+                       if (unlikely(hash < pos))
+                               /*
+                                * Skip until we find target hash value.
+                                */
+                               continue;
+
+                       namelen = le16_to_cpu(ent->lde_namelen);
+                       if (unlikely(namelen == 0))
+                               /*
+                                * Skip dummy record.
+                                */
+                               continue;
+
+                       name = ent->lde_name;
+                       if (name[0] == '.') {
+                               if (namelen == 1) {
+                                       /*
+                                        * skip "."
+                                        */
+                                       continue;
+                               } else if (name[1] == '.' && namelen == 2) {
+                                       /*
+                                        * skip ".."
+                                        */
+                                       continue;
+                               } else if (!sai->sai_ls_all) {
+                                       /*
+                                        * skip hidden files.
+                                        */
+                                       sai->sai_skip_hidden++;
+                                       continue;
                                }
-                               spin_unlock(&plli->lli_agl_lock);
+                       }
 
-                                goto keep_it;
-                        }
+                       /*
+                        * don't stat-ahead first entry.
+                        */
+                       if (unlikely(++first == 1))
+                               continue;
+
+                       /* wait for spare statahead window */
+                       do {
+                               l_wait_event(thread->t_ctl_waitq,
+                                            !sa_sent_full(sai) ||
+                                            sa_has_callback(sai) ||
+                                            !agl_list_empty(sai) ||
+                                            !thread_is_running(thread),
+                                            &lwi);
+
+                               sa_handle_callback(sai);
+                       } while (sa_sent_full(sai) &&
+                                thread_is_running(thread));
+
+                       sa_statahead(parent, name, namelen);
+               }
 
-do_it:
-                        ll_statahead_one(parent, name, namelen);
-                }
-                pos = le64_to_cpu(dp->ldp_hash_end);
-                if (pos == MDS_DIR_END_OFF) {
-                        /*
-                         * End of directory reached.
-                         */
-                        ll_release_page(page, 0);
-                        while (1) {
-                                l_wait_event(thread->t_ctl_waitq,
-                                             !sa_received_empty(sai) ||
-                                             sai->sai_sent == sai->sai_replied||
-                                             !thread_is_running(thread),
-                                             &lwi);
-
-                                while (!sa_received_empty(sai))
-                                        do_statahead_interpret(sai, NULL);
-
-                                if (unlikely(!thread_is_running(thread)))
-                                        GOTO(out, rc = 0);
-
-                                if (sai->sai_sent == sai->sai_replied &&
-                                    sa_received_empty(sai))
-                                        break;
-                        }
-
-                       spin_lock(&plli->lli_agl_lock);
-                       while (!agl_list_empty(sai) &&
-                              thread_is_running(thread)) {
-                               clli = agl_first_entry(sai);
-                               cfs_list_del_init(&clli->lli_agl_list);
-                               spin_unlock(&plli->lli_agl_lock);
-                               ll_agl_trigger(&clli->lli_vfs_inode, sai);
-                               spin_lock(&plli->lli_agl_lock);
-                       }
-                       spin_unlock(&plli->lli_agl_lock);
+               pos = le64_to_cpu(dp->ldp_hash_end);
+               ll_release_page(dir, page,
+                               le32_to_cpu(dp->ldp_flags) & LDF_COLLIDE);
+
+               if (sa_low_hit(sai)) {
+                       rc = -EFAULT;
+                       atomic_inc(&sbi->ll_sa_wrong);
+                       CDEBUG(D_READA, "Statahead for dir "DFID" hit "
+                              "ratio too low: hit/miss "LPU64"/"LPU64
+                              ", sent/replied "LPU64"/"LPU64", stopping "
+                              "statahead thread: pid %d\n",
+                              PFID(&lli->lli_fid), sai->sai_hit,
+                              sai->sai_miss, sai->sai_sent,
+                              sai->sai_replied, current_pid());
+                       break;
+               }
+       }
+       ll_dir_chain_fini(&chain);
+       ll_finish_md_op_data(op_data);
 
-                        GOTO(out, rc = 0);
-                } else if (1) {
-                        /*
-                         * chain is exhausted.
-                         * Normal case: continue to the next page.
-                         */
-                        ll_release_page(page, le32_to_cpu(dp->ldp_flags) &
-                                              LDF_COLLIDE);
-                        sai->sai_in_readpage = 1;
-                       page = ll_get_dir_page(dir, pos, &chain);
-                        sai->sai_in_readpage = 0;
-                } else {
-                        LASSERT(le32_to_cpu(dp->ldp_flags) & LDF_COLLIDE);
-                        ll_release_page(page, 1);
-                        /*
-                         * go into overflow page.
-                         */
-                }
-        }
-        EXIT;
+       if (rc < 0) {
+               spin_lock(&lli->lli_sa_lock);
+               thread_set_flags(thread, SVC_STOPPING);
+               lli->lli_sa_enabled = 0;
+               spin_unlock(&lli->lli_sa_lock);
+       }
+
+       /* statahead is finished, but statahead entries need to be cached, wait
+        * for file release to stop me. */
+       while (thread_is_running(thread)) {
+               l_wait_event(thread->t_ctl_waitq,
+                            sa_has_callback(sai) ||
+                            !agl_list_empty(sai) ||
+                            !thread_is_running(thread),
+                            &lwi);
+
+               sa_handle_callback(sai);
+       }
 
+       EXIT;
 out:
-        if (sai->sai_agl_valid) {
-               spin_lock(&plli->lli_agl_lock);
+       if (sai->sai_agl_valid) {
+               spin_lock(&lli->lli_agl_lock);
                thread_set_flags(agl_thread, SVC_STOPPING);
-               spin_unlock(&plli->lli_agl_lock);
-                cfs_waitq_signal(&agl_thread->t_ctl_waitq);
+               spin_unlock(&lli->lli_agl_lock);
+               wake_up(&agl_thread->t_ctl_waitq);
+
+               CDEBUG(D_READA, "stop agl thread: sai %p pid %u\n",
+                      sai, (unsigned int)agl_thread->t_pid);
+               l_wait_event(agl_thread->t_ctl_waitq,
+                            thread_is_stopped(agl_thread),
+                            &lwi);
+       } else {
+               /* Set agl_thread flags anyway. */
+               thread_set_flags(agl_thread, SVC_STOPPED);
+       }
 
-                CDEBUG(D_READA, "stop agl thread: [pid %d]\n",
-                       cfs_curproc_pid());
-                l_wait_event(agl_thread->t_ctl_waitq,
-                             thread_is_stopped(agl_thread),
-                             &lwi);
-        } else {
-                /* Set agl_thread flags anyway. */
-                thread_set_flags(&sai->sai_agl_thread, SVC_STOPPED);
-        }
-        ll_dir_chain_fini(&chain);
-       spin_lock(&plli->lli_sa_lock);
-       if (!sa_received_empty(sai)) {
-               thread_set_flags(thread, SVC_STOPPING);
-               spin_unlock(&plli->lli_sa_lock);
+       /* wait for inflight statahead RPCs to finish, and then we can free sai
+        * safely because statahead RPC will access sai data */
+       while (sai->sai_sent != sai->sai_replied) {
+               /* in case we're not woken up, timeout wait */
+               lwi = LWI_TIMEOUT(HZ >> 3, NULL, NULL);
+               l_wait_event(thread->t_ctl_waitq,
+                       sai->sai_sent == sai->sai_replied, &lwi);
+       }
 
-               /* To release the resources held by received entries. */
-               while (!sa_received_empty(sai))
-                       do_statahead_interpret(sai, NULL);
+       /* release resources held by statahead RPCs */
+       sa_handle_callback(sai);
 
-               spin_lock(&plli->lli_sa_lock);
-       }
+       spin_lock(&lli->lli_sa_lock);
        thread_set_flags(thread, SVC_STOPPED);
-       spin_unlock(&plli->lli_sa_lock);
-        cfs_waitq_signal(&sai->sai_waitq);
-        cfs_waitq_signal(&thread->t_ctl_waitq);
+       spin_unlock(&lli->lli_sa_lock);
+
+       wake_up(&sai->sai_waitq);
+       wake_up(&thread->t_ctl_waitq);
         ll_sai_put(sai);
-        dput(parent);
-        CDEBUG(D_READA, "statahead thread stopped: [pid %d] [parent %.*s]\n",
-               cfs_curproc_pid(), parent->d_name.len, parent->d_name.name);
-        return rc;
+       CDEBUG(D_READA, "statahead thread stopped: sai %p, parent %.*s\n",
+              sai, parent->d_name.len, parent->d_name.name);
+       dput(parent);
+       return rc;
 }
 
-/**
- * called in ll_file_release().
- */
-void ll_stop_statahead(struct inode *dir, void *key)
+/* authorize opened dir handle @key to statahead later */
+void ll_authorize_statahead(struct inode *dir, void *key)
 {
        struct ll_inode_info *lli = ll_i2info(dir);
 
-       if (unlikely(key == NULL))
-               return;
-
        spin_lock(&lli->lli_sa_lock);
-       if (lli->lli_opendir_key != key || lli->lli_opendir_pid == 0) {
-               spin_unlock(&lli->lli_sa_lock);
-                return;
-        }
-
-        lli->lli_opendir_key = NULL;
+       if (lli->lli_opendir_key == NULL && lli->lli_sai == NULL) {
+               /*
+                * if lli_sai is not NULL, it means previous statahead is not
+                * finished yet, we'd better not start a new statahead for now.
+                */
+               LASSERT(lli->lli_opendir_pid == 0);
+               lli->lli_opendir_key = key;
+               lli->lli_opendir_pid = current_pid();
+               lli->lli_sa_enabled = 1;
+       }
+       spin_unlock(&lli->lli_sa_lock);
+}
 
-        if (lli->lli_sai) {
-                struct l_wait_info lwi = { 0 };
-                struct ptlrpc_thread *thread = &lli->lli_sai->sai_thread;
+/* deauthorize opened dir handle @key to statahead, but statahead thread may
+ * still be running, notify it to quit. */
+void ll_deauthorize_statahead(struct inode *dir, void *key)
+{
+       struct ll_inode_info *lli = ll_i2info(dir);
+       struct ll_statahead_info *sai;
 
-                if (!thread_is_stopped(thread)) {
-                        thread_set_flags(thread, SVC_STOPPING);
-                       spin_unlock(&lli->lli_sa_lock);
-                       cfs_waitq_signal(&thread->t_ctl_waitq);
+       LASSERT(lli->lli_opendir_key == key);
+       LASSERT(lli->lli_opendir_pid != 0);
 
-                       CDEBUG(D_READA, "stop statahead thread: [pid %d]\n",
-                              cfs_curproc_pid());
-                       l_wait_event(thread->t_ctl_waitq,
-                                    thread_is_stopped(thread),
-                                    &lwi);
-               } else {
-                       spin_unlock(&lli->lli_sa_lock);
-               }
+       CDEBUG(D_READA, "deauthorize statahead for "DFID"\n",
+               PFID(&lli->lli_fid));
 
+       spin_lock(&lli->lli_sa_lock);
+       lli->lli_opendir_key = NULL;
+       lli->lli_opendir_pid = 0;
+       lli->lli_sa_enabled = 0;
+       sai = lli->lli_sai;
+       if (sai != NULL && thread_is_running(&sai->sai_thread)) {
                /*
-                * Put the ref which was held when first statahead_enter.
-                * It maybe not the last ref for some statahead requests
-                * maybe inflight.
+                * statahead thread may not quit yet because it needs to cache
+                * entries, now it's time to tell it to quit.
                 */
-               ll_sai_put(lli->lli_sai);
-       } else {
-               lli->lli_opendir_pid = 0;
-               spin_unlock(&lli->lli_sa_lock);
+               thread_set_flags(&sai->sai_thread, SVC_STOPPING);
+               wake_up(&sai->sai_thread.t_ctl_waitq);
        }
+       spin_unlock(&lli->lli_sa_lock);
 }
 
 enum {
@@ -1389,355 +1254,346 @@ enum {
 
 static int is_first_dirent(struct inode *dir, struct dentry *dentry)
 {
-        struct ll_dir_chain   chain;
-        struct qstr          *target = &dentry->d_name;
-        struct page          *page;
-        __u64                 pos    = 0;
-        int                   dot_de;
-        int                   rc     = LS_NONE_FIRST_DE;
-        ENTRY;
+       struct ll_dir_chain   chain;
+       struct qstr          *target = &dentry->d_name;
+       struct md_op_data    *op_data;
+       int                   dot_de;
+       struct page          *page = NULL;
+       int                   rc     = LS_NONE_FIRST_DE;
+       __u64                 pos = 0;
+       ENTRY;
+
+       op_data = ll_prep_md_op_data(NULL, dir, dir, NULL, 0, 0,
+                                    LUSTRE_OPC_ANY, dir);
+       if (IS_ERR(op_data))
+               RETURN(PTR_ERR(op_data));
+       /**
+        *FIXME choose the start offset of the readdir
+        */
+       op_data->op_stripe_offset = 0;
+       op_data->op_max_pages = ll_i2sbi(dir)->ll_md_brw_pages;
 
-        ll_dir_chain_init(&chain);
-       page = ll_get_dir_page(dir, pos, &chain);
+       ll_dir_chain_init(&chain);
+       page = ll_get_dir_page(dir, op_data, 0, &chain);
+
+       while (1) {
+               struct lu_dirpage *dp;
+               struct lu_dirent  *ent;
+
+               if (IS_ERR(page)) {
+                       struct ll_inode_info *lli = ll_i2info(dir);
+
+                       rc = PTR_ERR(page);
+                       CERROR("%s: reading dir "DFID" at "LPU64
+                              "opendir_pid = %u : rc = %d\n",
+                              ll_get_fsname(dir->i_sb, NULL, 0),
+                              PFID(ll_inode2fid(dir)), pos,
+                              lli->lli_opendir_pid, rc);
+                       break;
+               }
 
-        while (1) {
-                struct lu_dirpage *dp;
-                struct lu_dirent  *ent;
+               dp = page_address(page);
+               for (ent = lu_dirent_start(dp); ent != NULL;
+                    ent = lu_dirent_next(ent)) {
+                       __u64 hash;
+                       int namelen;
+                       char *name;
+
+                       hash = le64_to_cpu(ent->lde_hash);
+                       /* The ll_get_dir_page() can return any page containing
+                        * the given hash which may be not the start hash. */
+                       if (unlikely(hash < pos))
+                               continue;
+
+                       namelen = le16_to_cpu(ent->lde_namelen);
+                       if (unlikely(namelen == 0))
+                               /*
+                                * skip dummy record.
+                                */
+                               continue;
+
+                       name = ent->lde_name;
+                       if (name[0] == '.') {
+                               if (namelen == 1)
+                                       /*
+                                        * skip "."
+                                        */
+                                       continue;
+                               else if (name[1] == '.' && namelen == 2)
+                                       /*
+                                        * skip ".."
+                                        */
+                                       continue;
+                               else
+                                       dot_de = 1;
+                       } else {
+                               dot_de = 0;
+                       }
 
-                if (IS_ERR(page)) {
-                        struct ll_inode_info *lli = ll_i2info(dir);
+                       if (dot_de && target->name[0] != '.') {
+                               CDEBUG(D_READA, "%.*s skip hidden file %.*s\n",
+                                      target->len, target->name,
+                                      namelen, name);
+                               continue;
+                       }
 
-                        rc = PTR_ERR(page);
-                        CERROR("error reading dir "DFID" at "LPU64": "
-                               "[rc %d] [parent %u]\n",
-                               PFID(ll_inode2fid(dir)), pos,
-                               rc, lli->lli_opendir_pid);
-                        break;
-                }
-
-                dp = page_address(page);
-                for (ent = lu_dirent_start(dp); ent != NULL;
-                     ent = lu_dirent_next(ent)) {
-                        __u64 hash;
-                        int namelen;
-                        char *name;
-
-                        hash = le64_to_cpu(ent->lde_hash);
-                        /* The ll_get_dir_page() can return any page containing
-                         * the given hash which may be not the start hash. */
-                        if (unlikely(hash < pos))
-                                continue;
-
-                        namelen = le16_to_cpu(ent->lde_namelen);
-                        if (unlikely(namelen == 0))
-                                /*
-                                 * skip dummy record.
-                                 */
-                                continue;
-
-                        name = ent->lde_name;
-                        if (name[0] == '.') {
-                                if (namelen == 1)
-                                        /*
-                                         * skip "."
-                                         */
-                                        continue;
-                                else if (name[1] == '.' && namelen == 2)
-                                        /*
-                                         * skip ".."
-                                         */
-                                        continue;
-                                else
-                                        dot_de = 1;
-                        } else {
-                                dot_de = 0;
-                        }
-
-                        if (dot_de && target->name[0] != '.') {
-                                CDEBUG(D_READA, "%.*s skip hidden file %.*s\n",
-                                       target->len, target->name,
-                                       namelen, name);
-                                continue;
-                        }
-
-                        if (target->len != namelen ||
-                            memcmp(target->name, name, namelen) != 0)
-                                rc = LS_NONE_FIRST_DE;
-                        else if (!dot_de)
-                                rc = LS_FIRST_DE;
-                        else
-                                rc = LS_FIRST_DOT_DE;
-
-                        ll_release_page(page, 0);
-                        GOTO(out, rc);
-                }
-                pos = le64_to_cpu(dp->ldp_hash_end);
-                if (pos == MDS_DIR_END_OFF) {
-                        /*
-                         * End of directory reached.
-                         */
-                        ll_release_page(page, 0);
-                        break;
-                } else if (1) {
-                        /*
-                         * chain is exhausted
-                         * Normal case: continue to the next page.
-                         */
-                        ll_release_page(page, le32_to_cpu(dp->ldp_flags) &
-                                              LDF_COLLIDE);
-                       page = ll_get_dir_page(dir, pos, &chain);
-                } else {
-                        /*
-                         * go into overflow page.
-                         */
-                        LASSERT(le32_to_cpu(dp->ldp_flags) & LDF_COLLIDE);
-                        ll_release_page(page, 1);
-                }
-        }
-        EXIT;
+                       if (target->len != namelen ||
+                           memcmp(target->name, name, namelen) != 0)
+                               rc = LS_NONE_FIRST_DE;
+                       else if (!dot_de)
+                               rc = LS_FIRST_DE;
+                       else
+                               rc = LS_FIRST_DOT_DE;
 
+                       ll_release_page(dir, page, false);
+                       GOTO(out, rc);
+               }
+               pos = le64_to_cpu(dp->ldp_hash_end);
+               if (pos == MDS_DIR_END_OFF) {
+                       /*
+                        * End of directory reached.
+                        */
+                       ll_release_page(dir, page, false);
+                       GOTO(out, rc);
+               } else {
+                       /*
+                        * chain is exhausted
+                        * Normal case: continue to the next page.
+                        */
+                       ll_release_page(dir, page, le32_to_cpu(dp->ldp_flags) &
+                                             LDF_COLLIDE);
+                       page = ll_get_dir_page(dir, op_data, pos, &chain);
+               }
+       }
+       EXIT;
 out:
-        ll_dir_chain_fini(&chain);
+       ll_dir_chain_fini(&chain);
+       ll_finish_md_op_data(op_data);
         return rc;
 }
 
-static void
-ll_sai_unplug(struct ll_statahead_info *sai, struct ll_sa_entry *entry)
+static int revalidate_statahead_dentry(struct inode *dir,
+                                       struct ll_statahead_info *sai,
+                                       struct dentry **dentryp,
+                                       int only_unplug)
 {
-        struct ptlrpc_thread *thread = &sai->sai_thread;
-        struct ll_sb_info    *sbi    = ll_i2sbi(sai->sai_inode);
-        int                   hit;
-        ENTRY;
-
-        if (entry != NULL && entry->se_stat == SA_ENTRY_SUCC)
-                hit = 1;
-        else
-                hit = 0;
-
-        ll_sa_entry_fini(sai, entry);
-        if (hit) {
-                sai->sai_hit++;
-                sai->sai_consecutive_miss = 0;
-                sai->sai_max = min(2 * sai->sai_max, sbi->ll_sa_max);
-        } else {
-                struct ll_inode_info *lli = ll_i2info(sai->sai_inode);
-
-                sai->sai_miss++;
-                sai->sai_consecutive_miss++;
-                if (sa_low_hit(sai) && thread_is_running(thread)) {
-                        atomic_inc(&sbi->ll_sa_wrong);
-                        CDEBUG(D_READA, "Statahead for dir "DFID" hit "
-                               "ratio too low: hit/miss "LPU64"/"LPU64
-                               ", sent/replied "LPU64"/"LPU64", stopping "
-                               "statahead thread: pid %d\n",
-                               PFID(&lli->lli_fid), sai->sai_hit,
-                               sai->sai_miss, sai->sai_sent,
-                               sai->sai_replied, cfs_curproc_pid());
-                       spin_lock(&lli->lli_sa_lock);
-                       if (!thread_is_stopped(thread))
-                               thread_set_flags(thread, SVC_STOPPING);
-                       spin_unlock(&lli->lli_sa_lock);
+       struct sa_entry *entry = NULL;
+       struct l_wait_info lwi = { 0 };
+       int rc = 0;
+       ENTRY;
+
+       if ((*dentryp)->d_name.name[0] == '.') {
+               if (sai->sai_ls_all ||
+                   sai->sai_miss_hidden >= sai->sai_skip_hidden) {
+                       /*
+                        * Hidden dentry is the first one, or statahead
+                        * thread does not skip so many hidden dentries
+                        * before "sai_ls_all" enabled as below.
+                        */
+               } else {
+                       if (!sai->sai_ls_all)
+                               /*
+                                * It maybe because hidden dentry is not
+                                * the first one, "sai_ls_all" was not
+                                * set, then "ls -al" missed. Enable
+                                * "sai_ls_all" for such case.
+                                */
+                               sai->sai_ls_all = 1;
+
+                       /*
+                        * Such "getattr" has been skipped before
+                        * "sai_ls_all" enabled as above.
+                        */
+                       sai->sai_miss_hidden++;
+                       RETURN(-EAGAIN);
                }
        }
 
-       if (!thread_is_stopped(thread))
-               cfs_waitq_signal(&thread->t_ctl_waitq);
-
-       EXIT;
-}
-
-/**
- * Start statahead thread if this is the first dir entry.
- * Otherwise if a thread is started already, wait it until it is ahead of me.
- * \retval 1       -- find entry with lock in cache, the caller needs to do
- *                    nothing.
- * \retval 0       -- find entry in cache, but without lock, the caller needs
- *                    refresh from MDS.
- * \retval others  -- the caller need to process as non-statahead.
- */
-int do_statahead_enter(struct inode *dir, struct dentry **dentryp,
-                       int only_unplug)
-{
-        struct ll_inode_info     *lli   = ll_i2info(dir);
-        struct ll_statahead_info *sai   = lli->lli_sai;
-        struct dentry            *parent;
-        struct ll_sa_entry       *entry;
-        struct ptlrpc_thread     *thread;
-        struct l_wait_info        lwi   = { 0 };
-        int                       rc    = 0;
-        ENTRY;
-
-        LASSERT(lli->lli_opendir_pid == cfs_curproc_pid());
-
-        if (sai) {
-                thread = &sai->sai_thread;
-                if (unlikely(thread_is_stopped(thread) &&
-                             cfs_list_empty(&sai->sai_entries_stated))) {
-                        /* to release resource */
-                        ll_stop_statahead(dir, lli->lli_opendir_key);
-                        RETURN(-EAGAIN);
-                }
-
-                if ((*dentryp)->d_name.name[0] == '.') {
-                        if (sai->sai_ls_all ||
-                            sai->sai_miss_hidden >= sai->sai_skip_hidden) {
-                                /*
-                                 * Hidden dentry is the first one, or statahead
-                                 * thread does not skip so many hidden dentries
-                                 * before "sai_ls_all" enabled as below.
-                                 */
-                        } else {
-                                if (!sai->sai_ls_all)
-                                        /*
-                                         * It maybe because hidden dentry is not
-                                         * the first one, "sai_ls_all" was not
-                                         * set, then "ls -al" missed. Enable
-                                         * "sai_ls_all" for such case.
-                                         */
-                                        sai->sai_ls_all = 1;
-
-                                /*
-                                 * Such "getattr" has been skipped before
-                                 * "sai_ls_all" enabled as above.
-                                 */
-                                sai->sai_miss_hidden++;
-                                RETURN(-EAGAIN);
-                        }
-                }
-
-                entry = ll_sa_entry_get_byname(sai, &(*dentryp)->d_name);
-                if (entry == NULL || only_unplug) {
-                        ll_sai_unplug(sai, entry);
-                        RETURN(entry ? 1 : -EAGAIN);
-                }
+       entry = sa_get(sai, &(*dentryp)->d_name);
+       if (entry == NULL || only_unplug) {
+               sa_put(sai, entry);
+               RETURN(entry ? 1 : -EAGAIN);
+       }
 
-                while (!ll_sa_entry_stated(entry) &&
-                       sai->sai_in_readpage &&
-                       !sa_received_empty(sai))
-                        do_statahead_interpret(sai, entry);
-
-                if (!ll_sa_entry_stated(entry)) {
-                        sai->sai_index_wait = entry->se_index;
-                        lwi = LWI_TIMEOUT_INTR(cfs_time_seconds(30), NULL,
-                                               LWI_ON_SIGNAL_NOOP, NULL);
-                        rc = l_wait_event(sai->sai_waitq,
-                                          ll_sa_entry_stated(entry) ||
-                                          thread_is_stopped(thread),
-                                          &lwi);
-                        if (rc < 0) {
-                                ll_sai_unplug(sai, entry);
-                                RETURN(-EAGAIN);
-                        }
-                }
+       /* if statahead is busy in readdir, help it do post-work */
+       if (!sa_ready(entry) && sai->sai_in_readpage)
+               sa_handle_callback(sai);
+
+       if (!sa_ready(entry)) {
+               sai->sai_index_wait = entry->se_index;
+               lwi = LWI_TIMEOUT_INTR(cfs_time_seconds(30), NULL,
+                                       LWI_ON_SIGNAL_NOOP, NULL);
+               rc = l_wait_event(sai->sai_waitq,
+                               sa_ready(entry) ||
+                               thread_is_stopped(&sai->sai_thread),
+                               &lwi);
+               if (rc < 0) {
+                       sa_put(sai, entry);
+                       RETURN(-EAGAIN);
+               }
+       }
 
-                if (entry->se_stat == SA_ENTRY_SUCC &&
-                    entry->se_inode != NULL) {
-                        struct inode *inode = entry->se_inode;
-                        struct lookup_intent it = { .it_op = IT_GETATTR,
-                                                    .d.lustre.it_lock_handle =
-                                                     entry->se_handle };
-                       __u64 bits;
-
-                       rc = md_revalidate_lock(ll_i2mdexp(dir), &it,
-                                               ll_inode2fid(inode), &bits);
-                       if (rc == 1) {
-                               if ((*dentryp)->d_inode == NULL) {
-                                       *dentryp = ll_splice_alias(inode,
-                                                                  *dentryp);
-                                } else if ((*dentryp)->d_inode != inode) {
-                                        /* revalidate, but inode is recreated */
-                                        CDEBUG(D_READA,
-                                              "stale dentry %.*s inode %lu/%u, "
-                                              "statahead inode %lu/%u\n",
-                                              (*dentryp)->d_name.len,
-                                              (*dentryp)->d_name.name,
-                                              (*dentryp)->d_inode->i_ino,
-                                              (*dentryp)->d_inode->i_generation,
-                                              inode->i_ino,
-                                              inode->i_generation);
-                                        ll_sai_unplug(sai, entry);
-                                        RETURN(-ESTALE);
-                                } else {
-                                       iput(inode);
+       if (entry->se_state == SA_ENTRY_SUCC && entry->se_inode != NULL) {
+               struct inode *inode = entry->se_inode;
+               struct lookup_intent it = { .it_op = IT_GETATTR,
+                                           .d.lustre.it_lock_handle =
+                                               entry->se_handle };
+               __u64 bits;
+
+               rc = md_revalidate_lock(ll_i2mdexp(dir), &it,
+                                       ll_inode2fid(inode), &bits);
+               if (rc == 1) {
+                       if ((*dentryp)->d_inode == NULL) {
+                               struct dentry *alias;
+
+                               alias = ll_splice_alias(inode, *dentryp);
+                               if (IS_ERR(alias)) {
+                                       sa_put(sai, entry);
+                                       RETURN(PTR_ERR(alias));
                                }
-                               entry->se_inode = NULL;
-
-                               if ((bits & MDS_INODELOCK_LOOKUP) &&
-                                   d_lustre_invalid(*dentryp))
-                                       d_lustre_revalidate(*dentryp);
-                                ll_intent_release(&it);
-                        }
-                }
-
-                ll_sai_unplug(sai, entry);
-                RETURN(rc);
-        }
+                               *dentryp = alias;
+                       } else if ((*dentryp)->d_inode != inode) {
+                               /* revalidate, but inode is recreated */
+                               CDEBUG(D_READA,
+                                       "%s: stale dentry %.*s inode "
+                                       DFID", statahead inode "DFID
+                                       "\n",
+                                       ll_get_fsname((*dentryp)->d_inode->i_sb,
+                                                     NULL, 0),
+                                       (*dentryp)->d_name.len,
+                                       (*dentryp)->d_name.name,
+                                       PFID(ll_inode2fid((*dentryp)->d_inode)),
+                                       PFID(ll_inode2fid(inode)));
+                               sa_put(sai, entry);
+                               RETURN(-ESTALE);
+                       } else {
+                               iput(inode);
+                       }
+                       entry->se_inode = NULL;
 
-        /* I am the "lli_opendir_pid" owner, only me can set "lli_sai". */
-        rc = is_first_dirent(dir, *dentryp);
-        if (rc == LS_NONE_FIRST_DE)
-                /* It is not "ls -{a}l" operation, no need statahead for it. */
-                GOTO(out, rc = -EAGAIN);
+                       if ((bits & MDS_INODELOCK_LOOKUP) &&
+                           d_lustre_invalid(*dentryp))
+                               d_lustre_revalidate(*dentryp);
+                       ll_intent_release(&it);
+               }
+       }
 
-        sai = ll_sai_alloc();
-        if (sai == NULL)
-                GOTO(out, rc = -ENOMEM);
+       sa_put(sai, entry);
+       RETURN(rc);
+}
 
-        sai->sai_ls_all = (rc == LS_FIRST_DOT_DE);
-        sai->sai_inode = igrab(dir);
-        if (unlikely(sai->sai_inode == NULL)) {
-                CWARN("Do not start stat ahead on dying inode "DFID"\n",
-                      PFID(&lli->lli_fid));
-                GOTO(out, rc = -ESTALE);
-        }
+static int start_statahead_thread(struct inode *dir, struct dentry *dentry)
+{
+       struct ll_inode_info *lli = ll_i2info(dir);
+       struct ll_statahead_info *sai = NULL;
+       struct dentry *parent;
+       struct ptlrpc_thread *thread;
+       struct l_wait_info lwi = { 0 };
+       struct task_struct *task;
+       int rc;
+       ENTRY;
+
+       /* I am the "lli_opendir_pid" owner, only me can set "lli_sai". */
+       rc = is_first_dirent(dir, dentry);
+       if (rc == LS_NONE_FIRST_DE)
+               /* It is not "ls -{a}l" operation, no need statahead for it. */
+               GOTO(out, rc = -EAGAIN);
+
+       sai = ll_sai_alloc();
+       if (sai == NULL)
+               GOTO(out, rc = -ENOMEM);
+
+       sai->sai_ls_all = (rc == LS_FIRST_DOT_DE);
+       sai->sai_inode = igrab(dir);
+       if (unlikely(sai->sai_inode == NULL)) {
+               CWARN("Do not start stat ahead on dying inode "DFID"\n",
+                       PFID(&lli->lli_fid));
+               GOTO(out, rc = -ESTALE);
+       }
 
-        /* get parent reference count here, and put it in ll_statahead_thread */
-        parent = dget((*dentryp)->d_parent);
-        if (unlikely(sai->sai_inode != parent->d_inode)) {
-                struct ll_inode_info *nlli = ll_i2info(parent->d_inode);
-
-                CWARN("Race condition, someone changed %.*s just now: "
-                      "old parent "DFID", new parent "DFID"\n",
-                      (*dentryp)->d_name.len, (*dentryp)->d_name.name,
-                      PFID(&lli->lli_fid), PFID(&nlli->lli_fid));
-                dput(parent);
-                iput(sai->sai_inode);
-                GOTO(out, rc = -EAGAIN);
-        }
+       /* get parent reference count here, and put it in ll_statahead_thread */
+       parent = dget(dentry->d_parent);
+       if (unlikely(sai->sai_inode != parent->d_inode)) {
+               struct ll_inode_info *nlli = ll_i2info(parent->d_inode);
+
+               CWARN("Race condition, someone changed %.*s just now: "
+                       "old parent "DFID", new parent "DFID"\n",
+                       dentry->d_name.len, dentry->d_name.name,
+                       PFID(&lli->lli_fid), PFID(&nlli->lli_fid));
+               dput(parent);
+               iput(sai->sai_inode);
+               GOTO(out, rc = -EAGAIN);
+       }
 
-        CDEBUG(D_READA, "start statahead thread: [pid %d] [parent %.*s]\n",
-               cfs_curproc_pid(), parent->d_name.len, parent->d_name.name);
+       CDEBUG(D_READA, "start statahead thread: sai %p, parent %.*s\n",
+              sai, parent->d_name.len, parent->d_name.name);
 
         lli->lli_sai = sai;
-        rc = cfs_create_thread(ll_statahead_thread, parent, 0);
-        thread = &sai->sai_thread;
-        if (rc < 0) {
-                CERROR("can't start ll_sa thread, rc: %d\n", rc);
-                dput(parent);
-                lli->lli_opendir_key = NULL;
-                thread_set_flags(thread, SVC_STOPPED);
-                thread_set_flags(&sai->sai_agl_thread, SVC_STOPPED);
-                ll_sai_put(sai);
-                LASSERT(lli->lli_sai == NULL);
-                RETURN(-EAGAIN);
-        }
 
-        l_wait_event(thread->t_ctl_waitq,
-                     thread_is_running(thread) || thread_is_stopped(thread),
-                     &lwi);
+       task = kthread_run(ll_statahead_thread, parent, "ll_sa_%u",
+                          lli->lli_opendir_pid);
+       thread = &sai->sai_thread;
+       if (IS_ERR(task)) {
+               rc = PTR_ERR(task);
+               CERROR("cannot start ll_sa thread: rc = %d\n", rc);
+               dput(parent);
+               lli->lli_opendir_key = NULL;
+               thread_set_flags(thread, SVC_STOPPED);
+               thread_set_flags(&sai->sai_agl_thread, SVC_STOPPED);
+               ll_sai_put(sai);
+               LASSERT(lli->lli_sai == NULL);
+               RETURN(-EAGAIN);
+       }
 
-        /*
-         * We don't stat-ahead for the first dirent since we are already in
-         * lookup.
-         */
-        RETURN(-EAGAIN);
+       l_wait_event(thread->t_ctl_waitq,
+                    thread_is_running(thread) || thread_is_stopped(thread),
+                    &lwi);
+       atomic_inc(&ll_i2sbi(parent->d_inode)->ll_sa_running);
+       ll_sai_put(sai);
+
+       /*
+        * We don't stat-ahead for the first dirent since we are already in
+        * lookup.
+        */
+       RETURN(-EAGAIN);
 
 out:
-        if (sai != NULL)
-                OBD_FREE_PTR(sai);
+       if (sai != NULL)
+               OBD_FREE_PTR(sai);
        spin_lock(&lli->lli_sa_lock);
        lli->lli_opendir_key = NULL;
        lli->lli_opendir_pid = 0;
+       lli->lli_sa_enabled = 0;
        spin_unlock(&lli->lli_sa_lock);
-       return rc;
+
+       RETURN(rc);
+}
+
+/**
+ * Start statahead thread if this is the first dir entry.
+ * Otherwise if a thread is started already, wait it until it is ahead of me.
+ * \retval 1       -- find entry with lock in cache, the caller needs to do
+ *                   nothing.
+ * \retval 0       -- find entry in cache, but without lock, the caller needs
+ *                   refresh from MDS.
+ * \retval others  -- the caller need to process as non-statahead.
+ */
+int do_statahead_enter(struct inode *dir, struct dentry **dentryp,
+                      int only_unplug)
+{
+       struct ll_statahead_info *sai;
+
+       sai = ll_sai_get(dir);
+       if (sai != NULL) {
+               int rc;
+
+               rc = revalidate_statahead_dentry(dir, sai, dentryp,
+                                                only_unplug);
+               CDEBUG(D_READA, "revalidate statahead %.*s: %d.\n",
+                       (*dentryp)->d_name.len, (*dentryp)->d_name.name, rc);
+               ll_sai_put(sai);
+               return rc;
+       }
+
+       return start_statahead_thread(dir, *dentryp);
 }